(1) Field of the Invention
This invention relates to shielded cable and, more particularly, to shielded cables molded of conductive loaded resin-based materials comprising micron conductive powders, micron conductive fibers, or a combination thereof, homogenized within a base resin when molded. This manufacturing process yields a conductive part or material usable within the EMF or electronic spectrum(s).
(2) Description of the Prior Art
Shielded cables are used in many applications where electromagnetic interference (EMI) or radio frequency interference (RFI) are concerns. By routing an electric signal in a shielded cable, the electric signal is protected from environmental sources of EMI/RFI that could be coupled onto the signal. Conversely, a shielded signal generates less radiated EMI/RMI emissions. Shielding of signals is frequently necessary in computers, audio electronics, avionics, and automotive electronics.
A shielded cable comprises three main components: signal wiring, shielding, and outer insulation. The signal wiring may comprise a single wire or multiple wires. For example, a coaxial shielded cable comprises a single signal wire. This wire comprises a conductor, typically a stranded or braided metal, that is surrounded by an insulating material. As another example, a twisted pair of wires, each comprising an insulated conductor, may be routed in the cable. Further, a large number of wires, each comprising an insulated conductor, may be routed in parallel through the cable. The shielding layer surrounds the signal wiring. In a typical application, this shielding layer is connected to a dc reference and, more typically, to ground. This shielding layer forms a Faraday cage that prevents EMI/RFI coupling between the shielded signal wiring and an external source and/or receiver. Finally, an outer jacket of insulating material surrounds the shielding layer. This outer jacket prevents shorting of the shielding layer and serves as an environmental barrier to protect the shielded cable from moisture and mechanical damage.
Several prior art inventions relate to shielded cable devices and methods of manufacture. U.S. Pat. No. 6,084,295 to Horiuchi et al describes a semiconductor device mounted on a circuit board. Wires are bonded between the semiconductor device and the circuit board. The wires comprise a gold wire surrounded by a resinous film insulator. After bonding, an electro-conductive resin film is formed over the wires and the semiconductor device. If the conductive resin film is set to a ground potential, then the bonded wires constitute a coaxial cable line. The conductive resin may contain silver filler. U.S. Patent Application Ser. No. 2002/0142653 to Hosaka et al shows a binding member, or connector, to connect a coaxial cable to an electrical signal. The binding member is constructed from a conductive resin material. The conductive resin material comprises a mixture of thermoplastic resin, lead-free solder, and powdered metal. U.S. Patent Application Ser. No. 2003/0090345 to Cooray et al describes a method to form a coaxial cable. A polymer/resin is first formed around a conductor. Then, a conductive layer is formed on the surface of the polymer/resin by a chemical reaction. The conductive layer forms the conductive shield for the cable. U.S. Pat. No. 6,265,667 to Stipes et al describes a method to manufacture a coaxial cable. An insulating layer is formed surrounding a central conductor by extrusion. A shielding layer is formed by wrapping metal foil and polyester tape and metal braid around the insulating layer. U.S. Pat. No. 5,946,798 to Buluschek discloses a method to manufacture a coaxial cable. The steps used in formation of the center conductor and the insulating layer are described. The insulating layer is formed by extrusion. U.S. Pat. No. 6,137,058 and U.S. Pat. No. 5,926,949 to Moe et al each describe a method to form a coaxial cable. A polyethylene foam is formed surrounding the center conductor by extrusion. A conductive shield is formed around the insulator by first forming a cylindrical shape around the insulator and then welding the seam. An outer jacket of polymer is then formed around the shield.